The present invention relates to a pretensioner device for automatically increasing the tension of an automotive seat belt.
An automotive scat is typically provided with a seat belt to restrain the vehicle occupant and prevent the occupant from being thrown forward at the time of a vehicle crash. A seat bolt is often incorporated with an emergency locking retractor (ELR) device for locking a winding shaft of the seat belt only at the time of a sudden stop and/or a vehicle crash while permitting free movement of the vehicle occupant under normal conditions. An ELR device locks up the winding shaft in an extremely short time upon detection of deceleration exceeding a prescribed level, and thereby prevents the seat belt from being paid out any further.
When the winding shaft is simply locked up, it is unavoidable to have a certain length of the seat belt resulting from the tightening of the length of the seat belt wound on the winding shaft to be paid out. In view of this problem, pretensioner devices of different kinds have been proposed, and one of such pretensioner devices is designed to pull the buckle attached to the seat belt in the direction to increase the tension of the seat belt so as to improve the restraining capability of the seat belt.
A typical buckle pretensioner device includes a base plate for attaching the device main body to one side of a seat, an arm having one end pivotally attached to the base plate and another end connected to a base end of a buckle, a power generator attached to the base plate to pull the buckle via a link mechanism and the arm, and a reverse preventing device for preventing the buckle from reversing its motion once it is pulled by the power generator.
Because the power generator typically uses the power generated by igniting a propellant received in a cylinder and pushing out a piston member with the resulting combustion gas, it is necessary that the linear motion of the piston is converted into a rotary motion of the arm, and this rotary motion is in turn converted into the linear motion of the buckle. Therefore, the efficiency of power transmission is dictated by the length of the arm, and the size and configuration of the link mechanism. For this reason, it becomes necessary to use a relatively large power generator, a long arm and a complex link mechanism, and these factors contributed to the increase in the size of the device. In the case of a front seat, the buckle is typically provided in a gap defined between a seat slide rail and a center console, and this gap is normally so small that the excessive size of the pretensioner device may require a redesigning of the seat and the entire layout of the passenger compartment.
The present invention was made in view of eliminating such problems of the prior art, and its primary object is to provide a seat belt pretensioner device which is compact, requires a small number of component parts and increase the reliability of operation, and is easy to assemble.
According to the present invention, such an object can be accomplished by providing a seat belt pretensioner device for moving a moveably supported seat belt buckle in a direction to increase the tension of a seat belt with a power generating device, and preventing the reversing of the movement of the buckle with a reverse preventing device, so as to automatically increase the tension of the seat belt in case of an impact situation such as a vehicle crash, characterized by that: the power generator is adapted to produce a pressure by means of a combustion of a propellant; a bladder-like member being expanded under the pressure produced from the power generator inside a chamber defined for guiding a direction of expansion of the bladder-like member to push a member supporting the buckle or, without using a bladder-like member, the member supporting the buckle being moved directly under pressure produced from the combustion of a propellant, to move the buckle in the direction to increase the tension of the seat belt. The reverse preventing device may comprise a plurality of ratchet teeth, and a plurality of pawl members which are adapted to engage the ratchet teeth at different timing.
Because the combustion gas pressure obtained from the power generating device can be directly applied to a buckle supporting member to actuate the buckle once the air-tightness of the parts for transmitting the pressure is ensured, a link mechanism is not required, and the number of component parts can be minimized. This contributes to the compact and light-weight design of the overall device. The movement of the buckle is achieved only through a change in the inner pressure of the chamber of the bladder-like member from the start to the end of its motion, and there is no cause for attenuation of power transmission due to the changing of the direction of a force by a link mechanism or other mechanical structures so that the size of the power generator can be minimized. In particular, according to an arrangement where a buckle support member supporting the buckle at a peripheral end thereof is rotatably supported by a seat, it is preferable to define a curved chamber along the rotational direction of the buckle support member for transmission of pressure.
Because the exposed parts consist of the buckle and a portion of the buckle support member, the interference with other components or vehicle occupants at the time of operation is minimized, and the layout and design of the device are both simplified.